The invention relates to a bipolar medical instrument.
Bipolar medical instruments are used to thermally cut, to coagulate or to cut and to coagulate tissue in a human or animal body under the influence of bipolar high-frequency current.
Bipolar instruments usually have a tubular shaft at whose distal end two jaw parts which are connected to one another in an articulated manner are arranged and can move relative to one another. A force transmission element which can move axially is arranged in the tubular shaft and is connected such that force can transmitted from a handle arranged at a proximal end to at least one jaw part, specifically the moving jaw part arranged at the distal end of the shaft. The jaw parts can be opened and closed by operation of the handle. The jaw parts each form an electrode, to which high-frequency current can be applied and which is of different polarity. Each jaw part has a separate associated electrical power supply line, which is in each case connected to one pole of the high-frequency voltage source. In most cases, the force transmission element acts as an electrically conductive connection to the moving jaw part while, in contrast, the tubular shaft acts as an electrically conductive connection to the other jaw part, irrespective of whether this is a moving or a stationary jaw part.
In such bipolar instruments it is necessary to provide not only adequate electrical insulation between the two electrical power supply lines, but in particular between the two jaw parts in the area of their articulation points, in order to avoid shorts via leakage current during use.
The electrical isolation of the two jaw parts from one another in the area of the joint has the problem that, particularly in the case of thin instruments, these isolating elements are very small and their mechanical strength is remarkably reduced. Since a high-frequency voltage in the order of magnitude of 2.5 kV is normally applied to jaw parts, this means, that, if the isolating elements are physically small, a voltage flashover will take place or a creepage current will be formed via the isolating element to the closest conductive component, which leads to a short.
In use, the jaw parts come into contact with electrically conductive liquids, in particular with body fluids, which can result in creepage currents via the isolating elements, thus leading to shorts. Arcs which damage the isolator can thus be formed.
US 2006/0259036 A1 discloses to design a electrically conductive first contact element for contacting the shaft and one of two jaw parts as an outer nose portion. A distal end of the nose portion is connected to one of the two jaw parts via a stake. The part which is connected with the shaft has the shape of a half pipe. A second contact element provides the electrical conductive connection between the rod-like force transmission element and the second jaw part. The second contact element is again designed as a nose portion connected at its distal end with the second jaw part. The second conductive element has a half pipe section too for connecting this second contact element with the rod-like force transmission element. Half pipe shaped insulators are disposed between the half pipe parts of the electrically conductive contact elements to insulate against the shaft and rod-like force transmission element, respectively.
When mounted, the two half pipe sections of the two contact elements are arranged close together. During use and in contact with electrically conductive liquids like body liquids, leakage currents can result between these two contact elements of different polarity.
It is therefore object of the present invention to develop a bipolar medical instrument such that the jaw parts are isolated reliably in the long term in the area of the joint, and such that this ensures that forces are transmitted in a mechanically robust form in the long term.